Bronze arrowheads form site T.21 of the North Sinai Archaeological Expedition of the Ben Gurion University contained magnesium in significant amounts, from 2.5 to 7.0%, although other bronze artifacts frorn the site did not. Ores and slags from the site contained magnesium but replication experirnents to reconstruct the method of introducing magnesium into the metal produced levels no higher than 0.5% in sand castings. The magnesium in the arrowheads was associated with the tin. It has the effect of hardening the alloy. -- AATA